Light olefin such as ethylene, propylene, etc. is widely useful in the petrochemical industry, and is an important chemical material that is utilized as a building block for chemical products (oxo-alcohol, acrylonitrile, propylene oxide, butanol, acrylic acid, etc.) and plastic products (polypropylene, ethylene-propylene rubber, etc.). In particular, propylene is a colorless compound having a low boiling point and is typically trading in a polymer grade (purity of at least about 99.5%), a chemical grade (purity of about 90 to 96%) and a refinery grade (purity of about 50 to 70%) .
Generally; such light olefin is obtained by subjecting naphtha or kerosene to pyrolysis (i.e. steam cracking) in the presence of water vapor. Although the demand for propylene is recently increasing, it is difficult to satisfy such high demand using a production process such as pyrolysis, and thus a variety of propylene synthesis methods (e.g. light fraction-catalytic cracking, etc.) are devised. The exemplary compositions (wt %) of the reaction products obtained through the above processes are shown in Table 1 below.
TABLE 1Reaction productReaction product of lightof steam crackingfraction-catalytic crackingMethane16.1313.91Ethylene32.0520.71Ethane2.918.93Propylene16.6522.06Propane0.353.04C410.948.97C55.717.81C6 or more14.1813.58Others1.080.99
As a widely available process these days, a propylene preparation process using dehydrogenation of propane is known, and propylene is synthesized by Scheme 1 below.

The dehyorogenation of propane is a process in which only propylene is selectively prepared from propane through a dehydrogecatioc reaction, and such a reaction is typically carried out for a short retention time through an endothermic reaction at a high temperature.
However, the propane dehydrogenation product is composed mainly of propylene, unreacted propane and hydrogen, and contains various byproducts. Thus, components having boiling points lower than that of a C3 gas mixture (propylene and propane) are conventionally separated through a low-temperature separation process (including a cooling process at about −100° C.) , and the C3 gas mixture is split into propylene and propane through multi-tray distilation using a C3 product splitter. Here, in the C3 product splitter, propylene is removed as the overhead stream, and propane is removed as the bottom stream (e.g. U.S. Pat. No. 6,218,589).
In this regard, FIG. 1 shows a conventional process of separating and recovering propylene from the propane dehydrogenation product through a low-temperature separation process and using a C3 product splitter.
As shown in this drawing, the propane-containing feedstock is transferred into a feedstock evaporator 1 so as to mainly separate propane, which is then heated (a gaseous phase) by means of a reaction feedstock heater 2 and fed into a dehydrogenation reactor 3 at a high temperature, and is thus converted into a propylene-containing reaction product. This reaction product undergoes heat exchange in a heat exchanger (a steam producer) 4, is pressurized in a reaction product compressor 5, is transferred into a product gas dryer knock-out drum 7 via a heat exchanger 6, and is then separated based on the boiling point. The overhead stream (gas product; of the knock-out drum 7 is sequentially passed through a product gas dryer 8 and a first product gas chiller 9 as a cooling system and is then transferred into a deethanizer 10. On the other hand, the bottom stream (liquid product) of the knock-out drum 7 is transferred into a deethanizer 10 through a deethanizer feed dryer 11. Here, fractions having the lowest boiling points throughout the processing, such as hydrogen, methane and so on, are separated from the first product gas chiller 9, pressurized in a hydrogen compressor 17, and recovered as hydrogen and fuel gas in a hydrogen refiner 18.
In the deethanizer 10, the C2 fraction is separated as the overhead stream, and fuel gas is recovered from she C2 fraction by means of a second product gas chiller 12. Here, separation is easily performed using an ethylene refrigeration compressor 16. The bottom stream of the deethanizer 10 is transferred into a C3 product splitter 14 through a product dryer treatment bed 13. In the C3 product splitter 14, propylene is separated as the overhead stream, transferred into a propylene refrigeration compressor 15, subjected to heat exchange in she second product gas chiller 12, and then recovered as a final product. Propane is separated at the bottom of the C3 product splitter 14 and is then recycled into the feedstock evaporator 1.
Meanwhile, the bottom stream of the feedstock evaporator 1 is transferred into a deoiler 19 to thus be split into propylene and a C4+, fraction. Here, the overhead fraction in the deoiler 19, namely propylene, is recovered into the feedstock evaporator 1, and the bottom fraction is transferred info a debutanizer 20. In she debutanizer 20, a C4 fraction is separated at the top thereof, and a C5+fraction is separated at the bottom thereof.
In the aforementioned conventional techniques, a difference in boiling points of individual materials is used upon separation of the dehydrogenation products, and thus a low-temperature separation process (cooling at about −100 ° C.) using an excess of energy is performed to remove components having boiling points lower than that of the C3 gas mixture, Furthermore, as shown in Table 2 below, propylene and paraffin have similar boiling points and relatively volatile properties, and the C3 product splitter 14 has to have a large number of distillation trays (about 200).
TABLE 2ClassificationBoiling point (° C.)NotePropylene−47.81 atmPropane−42.1
As described above, in the conventional method of separating the dehydrogenation products, the low-temperature separation process and the C3 product splitter need excessive energy, undesirably deteriorating processing efficiency. Thus, the development of energy-saving processes able to replace the low-temperature separation process and the C3 product splitter is required.
In order to replace the C3 product splitter, Korean Patent Application Publication No. 2012-0033368 discloses a process of separating propylene in which propylene is selectively adsorbed from a C3 mixture (a mixture of propane and propylene) among dehydrogenation products of propane and is separated from propane through displacement desorption using a desorbing agent. Specifically, this process (involving constant pressure or slight pressure fluctuations) is able to separate light olefin and paraffin without excessive pressure changes in the adsorber, in which olefin is selectively adsorbed to an adsorbing agent, and paraffin is passed, and is separated and recovered, via an additional still, and the adsorbed olefin is subjected to displacement desorption using a desorbing agent, and separated and recovered via an additional still.
Such a process is favorable because propylene and propane may be separated from each other at a constant pressure (or including slight pressure fluctuations) and at room temperature in lieu of the C3 product splitter required in the conventional techniques. Based on the results of research by the present inventors, however, when the above separation process is applied to the dehydrogenation products of propane, separation efficiency is decreased over time due to the deterioration of the adsorbing agent. Therefore, in order to separate tire dehydrogenation products of propane in the adsorption-displacement desorption manner, there is a need for methods of preventing the separation efficiency from decreasing due to the deterioration of the adsorbing agent.